The aim of this study is to design gas separator cyclones. Accordingly the design and simulation are performed by Gambit and FLUENT software programs respectively. To achieve good conclusion the results are collected in terms of efficiency and compared with Lapple’s analytical solution. As the results show there is a good approximation between the proposed Lapple’s analytical results in this study. In this study several variables are examined one of which is the residence time variable in the cyclone. The results showed that the difference between heavy and light particles’ residence time is only 2 or 3 seconds which indicates that the heavy particles play an important and determining role in the efficiency of cyclones because after the discharge of heavy particles the light particles’ output path is a direct route that only takes a few minutes. The next variable is velocity magnitude. In this study the changes in two types of light and heavy particle are shown in a graph. Another variable is the position of particles per second. In this study, the position of light and heavy particles is shown x-direction of a graph. And in the end the total pressure in the cyclone is investigated. The results showed that in the middle of the cyclone the pressure is reduced due to the vortex motion and it is increased near the walls.